In a magnetron sputtering apparatus, a magnet unit disposed on the back side of a cathode electrode supporting a target causes generation of magnetron on a discharge surface of the target to entrap a plasma, and, thus, to realize high density. Then, ions of the plasma generated in this apparatus collide with the target to thereby flick a target material. The target material is then adhered onto a substrate, whereby a thin film is formed.
Thus, a film formation rate strongly depends on an electric field and leakage magnetic field strength applied to a target. Especially, magnetron strength of a magnet unit strongly acts on a plasma density, and a film thickness distribution of a thin film formed on a substrate is influenced. In general, as the magnetron strength increases, the plasma density of the corresponding target is increased to increase a sputtering rate, and therefore, the film formation rate at the corresponding substrate position is also increased.
FIGS. 15A to 15D are explanatory views showing a magnetron sputtering apparatus that forms a film on a substrate while passing the substrate through the front of a target. For this type of pass-type film formation system, as shown in FIG. 15A, in general, a substrate 87 is passed so as to be perpendicular to the longitudinal direction of a rectangular target 86, as shown in FIG. 15A. Thus, as shown in FIG. 15C, the amount of sputtered particles from both ends in the longitudinal direction of the target 86 is small, and, as shown in FIG. 15B, the film thickness of the both ends of the substrate 87 is small, leading to deterioration of the film thickness distribution. Thus, as shown in FIG. 15D, in order to improve the deterioration of the film thickness distribution, the length in the longitudinal direction of the target 86 is increased, and a cathode electrode and a magnet unit 80 are extended so as to correspond to the target 86 to thereby respond to the deterioration of the film thickness distribution.
However, when the length of a target is increased in order to improve film thickness reduction at both ends of a substrate, not only consumption of a target material is increased, but also a running cost is increased.
Based on this point of view, in the prior art, there have been proposed various methods for adjusting the film thickness distribution of a thin film formed on a substrate. For example, a magnetic field strength on a target corresponding to a region on a substrate, in which the film thickness distribution of a thin film will be improved, is regulated by optimizing the height of each magnet, whereby the film thickness distribution is improved (see, Patent Document 1). Namely, in this film thickness adjusting method, the magnetic field strength on a target corresponding to a region on a substrate, in which the film thickness of a thin film is small, is increased, whereby the film formation rate is increased to increase the film thickness, and, thus, to improve the film thickness distribution.
There has been further provided a technique that in a magnet unit comprising a center magnet and an annular peripheral magnet surrounding the center magnet and having a polarity different from the polarity of the center magnet, the center magnet has T-shaped portions at its both ends, and magnetic tracks at the both ends are expanded, whereby the film thickness distribution of a thin film on a substrate is improved (see, Patent Document 2).